This invention relates to data processing systems; and in particular it relates to data processing systems which include some means for preventing the piracy of software programs.
Basically, every data processing system includes a digital computer which performs various tasks in response to a sequence of instructions called a program or software. Many different programs can be writtem for the same computer; and in each program, the sequence of instructions is differently arranged in accordance with the particular task that the computer is to perform. For example, one program can direct the computer to perform inventory operations, another program can direct the computer to perform payroll operations, etc.
Often, the programs which are written for a computer are very complex, comprise thousands of instructions, and represent a considerable investment in time and money. Therefore, efforts have been made in the prior art to prevent software from being stolen by software pirates. However, software is very easy to copy since it usually is stored on a magnetic tape or magnetic disk which is readily duplicated. Consequently, protecting software from piracy is difficult to achieve.
This problem of protecting software is most difficult for corporations which produce and license software programs, as a product, to many different customers. Each time a program is distributed under a license to a different customer, that customer becomes a potential software pirate. For example, the potential exists for a customer to copy the licensed software, terminate his license, and thereafter run the software copy. Also, the potential exists for the customer to copy the software and distribute it to third parties.
One of the prior art means which has been devised to prevent software piracy is described in U.S. Pat. Nos. 4,168,396 and 4,278,837 to Best. In these patents, each instruction of the program is encrypted and sent to the customer in the encrypted form. Then, when the program is to be run, it is read into the computer in encrypted form, decrypted inside of the computer, and executed.
In the Best system, the decrypted program is not available for copying since the program on the storage media is always encrypted. However, since each instruction must be decrypted prior to being executed, execution of the program is very slow. Further, the program only runs on specially constructed computers which do the decryption. These computers are only supplied by the software vendor; so the Best system does not even work in the typical case where the software customer wants to run a licensed program on a computer which he already owns.
Another prior art software protection system is described in U.S. Pat. 4,471,163 by Donald et al. In that system, the customer of a licensed program is supplied a program lock unit which performs a predetermined calculation on a number; and the program itself is modified to also perform the same calculation on the same number. Then the program compares the result of its calculations to the result obtained from the lock unit and the program stops if the two results are not equal.
A problem, however, with the Donald et al system is that the result of the calculation which the lock unit performs is passed to the computer over a conductor on which it could be read by a line analyzer. After being read, that same result could be generated by any memory circuit, such as a programmed read only memory. Thus a copy of the protected program could be made to run by simply replacing the lock unit with the read only memory.
Also in the Donald et al system, no further checks are made after the two results have been compared and the program has started to run. Therefore, one copy of the program can be started on a system to which the lock unit is attached, and thereafter the lock unit can be removed and transferred to another system whereupon another copy of the program can be started. Thus the protection system is not suitable for programs of a type which operate for long time periods--such as graphics programs which operate all day in an interactive fashion with an operator.
Another problem with the Donald et al system is that the customer of a licensed program must be given a copy of a key that contains several paramemters which the customer then enters via a keyboard into the lock unit. Those parameters are operated on by the lock unit to produce the result which the licensed program compares. However, having this key enables a customer of one program (program A) to copy his key and his program, and then give those copies to a customer of another program (program B). In return, the customer of program B can copy his program and his key, and given them to the customer of program A.
In view, therefore, of all of these prior art problems with protecting software, it is a primary object of the invention to provide an improved system for preventing software piracy in which these and other prior art deficiencies are overcome.